1. Field of the Invention
The present invention relates generally to a communication system. More particularly, the present invention relates to a method and system for controlling transmission power in an uplink of a communication system.
2. Description of the Related Art
Extensive research on the next generation communication system is being conducted to provide users with high-speed services having various Quality of Service (QoS) levels. Particularly, to increase data transmission capacity and improve QoS, the communication system controls transmission power in a downlink and an uplink such that a Base Station (BS) or a Mobile Station (MS) can have a Signal-to-Interference Ratio (SIR) necessary for data reception while using the minimum signal strength. By controlling transmission power in this manner, the communication system allows an MS having a low SIR to have higher transmission power in a service area where it can receive a communication service from the BS, thereby stably exchanging data with the BS. By doing so, the communication system improves QoS and prevents the MS from transmitting signals with unnecessarily high power, thereby reducing QoS degradation of an MS that uses the same frequency band and receives communication service from a neighboring BS.
This power control scheme controls transmission power of a transmitter such that when a receiver receives a transmission signal transmitted by a BS or an MS, the receiver can maintain its required SIR.
In particular, a communication system employing Orthogonal Frequency Division Multiplexing (OFDM)/Orthogonal Frequency Division Multiple Access (OFDMA) increases, as described above, the transmission power of signals within the area where no interference occurs between neighboring BSs, for example, within the area where the data being exchanged between neighboring BSs and MSs that receive communication services from the neighboring BSs do not act as an interference signal, thereby improving quality, i.e., QoS, of received signals. Therefore, the communication system needs to apply different power control conditions to an MS that has a high channel quality (i.e., an MS that is located in the center area of a BS in charge of a particular cell), and another MS that has a low channel quality (i.e., an MS that is located in the boundary area of the BS).
For example, when an MS located in the boundary area of a BS increases transmission power of its transmission signals for data exchange with the BS in charge of the cell where it is located, the MS induces an interference signal which is higher in strength by the transmission power, to a neighboring BS in charge of a cell neighboring the cell where it is currently located. Therefore, the BS allows the receiver, or the MS, to transmit signals with the minimum transmission power needed to maintain an SIR required for data exchange. However, when an MS located in the center area of the BS increases transmission power of its transmission signals, interference signals being applied to the neighboring BS in charge of a cell neighboring the cell where it is currently located are lower in strength. Therefore, the BS allows the MS to transmit signals with higher transmission power to improve reception quality, i.e., QoS, of transmission/reception signals. Accordingly, there is a need for a scheme of controlling transmission power for data exchange in the communication system in the manner described above.
In addition, the BS can reduce a Packet Error Rate (PER) of transmission/reception data by allowing the MS located in the center area of its own cell to transmit signals with higher transmission power, thereby reducing retransmission of packets due to reception failure of data and thus preventing waste of resources. By reducing the retransmission of packets, the BS can allocate the remaining resources to the MSs having a low channel quality and increase packet retransmission to the MSs having a low channel quality over the allocated channels, thereby improving performance of the communication system. Therefore, there is a need for a scheme of controlling transmission power in the communication system in the above-described manner.